President Barack Obama has defended the National Security Agency's surveillance programs, branding them a "modest encroachment" on privacy for the good of national defense.

On Friday, the U.S. president told reporters at Silicon Valley that the program, supervised by federal judges and authorized by Congress, is not about "listening to your telephone calls." Although the NSA can keep tabs on Americans' phone and Internet records, Obama said the correct "balance" has been kept between Big Brother-like spying and maintaining national security.

The president, now in his second term, said that he was skeptical about the programs when elected in 2008, but has come to the conclusion that such "modest encroachments on privacy" were worth it as a society, commenting:

"You can't have 100 percent security and also then have 100 percent privacy and zero inconvenience. We're going to have to make some choices as a society. There are trade-offs involved."

Unnamed U.S. officials told Reuters that law enforcement agencies, including the FBI and DOJ, are likely to open a criminal investigation into the leaking of documents to both The Guardian and Washington Post.

The NSA's whistleblower has been revealed as Edward Snowden, a 29-year-old who has worked as a former technical assistant for the CIA. Currently residing in Hong Kong to try and combat the U.S.'s expected reprisal for leaking information, Snowden said that despite having to leave a good job, home and family, he has "no regrets" and has "done nothing wrong."

"I understand that I will be made to suffer for my actions. I will be satisfied if the federation of secret law, unequal pardon and irresistible executive powers that rule the world that I love are revealed even for an instant," Snowden told The Guardian.

Last week, leaked secret court orders showing that the NSA was mining the phone records of millions of Verizon customers. Obama's comments now come after the Post and Guardian revealed details of the NSA's extensive surveillance, including programs Prism and Boundless Informant — the agency's means of data mining and cataloguing information.

The U.S. government is said to have collected almost three billion pieces of intelligence from U.S. computer networks in the 30-day period ending in March this year, as well as indexing almost 100 billion pieces worldwide.

A number of firms including Google, Apple, Yahoo and Facebook were labelled in the reports and granted "intelligence services direct access to the companies' servers." A number of companies have denied giving agencies "direct access," and the original Post story has been altered, potentially due to misinterpretation of leaked documents.

U.S. Director of National Intelligence James Clapper has said that the surveillance system is "important and entirely legal," and the behaviour of media outlets disclosing details of the program was "reprehensible."